The scientific name of small sixweeks grass is Vulpia microstachys (Nutt.) Benth. (Poaceae) [22,42,67,68,77,105].
In this review, small sixweeks grass varieties are referred to by the common
names given below. Varieties are:

Varieties often co-occur, and plants with intermediate characteristics are common [67,68].

The genus Vulpia is distinguished by annual life form and
cleistogamous
breeding habit, while Festuca is perennial and
chasmogamous [67].
Not all systematists support the separation of these closely aligned genera [33,84,109,111].

GENERAL DISTRIBUTION:
Small sixweeks grass is native, occurring from southern British Columbia and Montana south to New Mexico and
Baja California Norte. It also occurs on the Pacific slope of South America [22,57,105,114].

Distributions of the varieties overlap considerably. Eastwood small sixweeks
grass occurs from central Washington south to
northern Baja California and western Arizona [67]. Desert small sixweeks grass is
distributed from Washington east to western Montana and
south to northern Baja California, western Nevada, and southern New Mexico
[104,114]. Confusing small sixweeks grass is the least common variety, occurring
from south-central Washington to southern California. Pacific small sixweeks
grass occurs from Washington east to western Montana and south to Baja California Sur [65,104].
Plants database
provides a distributional map of small sixweeks grass and its infrataxa.

The following biogeographic classification systems are a guide
to where small sixweeks grass may occur. Except for the West Coast, precise distribution
information for small sixweeks grass is limited, and small sixweeks grass may
occur in ecosystems and plant communities that are not listed below.

California grasslands:
Small sixweeks grass is common to dominant in California's valleys and low foothills
[41]. On the San Joaquin Experimental Range near Fresno, it
was tallied as the 2nd most common grass over a 5-year period, comprising 9% to
17% cover [95].

It was also important in California's pristine valley grasslands. Small
sixweeks grass was probably abundant in California prairie in favorable years.
Historically, relative proportion of small sixweeks grass and other native
annual grasses was probably greatest on dry sites [40]. Grasslands on
serpentine soils
are among the few remnants of California prairie,
because nonnative annual grasses cannot compete with serpentine-adapted native
annual grasses on serpentine sites [47]. Pacific small sixweeks grass is
typically the dominant grass on serpentine soils [74].
Pacific small sixweeks grass is also noted on relict purple needlegrass (Nassella
pulchra) communities [89]. Holland [45] lists Eastwood and Pacific small
sixweeks grasses as dominant with serpentine reedgrass (Calamagrostis
ophitidis) on serpentine bunchgrasslands of the Coast Ranges, Sierra Nevada,
and Transverse Ranges.

Palouse prairie:
In 1913, Weaver [110] recorded Pacific
small sixweeks grass as the dominant annual of bluebunch wheatgrass
(Pseudoroegneria spicata) steppe in southeastern
Washington and adjacent Idaho. It occurred between bunchgrass interspaces at an
average density of 150 plants/m², and also occurred
in rimrock communities on upper slopes [110].

GENERAL BOTANICAL CHARACTERISTICS:
This description provides characteristics that may be relevant to fire ecology,
and is not meant for identification. Keys for species identification are
available (e.g., [42,67,111]). Lonard and Gould [67] provide a detailed key for identifying
infrataxa.

Small sixweeks grass is an annual. Culms are 5.9 to 30 inches (15-75 cm) long
and spreading, growing solitary or in small tufts. The inflorescence is a
narrow, 0.8- to 9-inch-long (2-24 cm), many-flowered panicle. Spikelets are 5.5
to 10 mm long. Lemmas are 4 to 9.5 mm long, and awned. Awns are relatively long
(3.5-20 mm) . The fruit is a caryopsis, ranging from 3.5 to 6 mm in length [22,42,56,67,111].

REGENERATION PROCESSES:
Because it is an annual, sixweeks grass regenerates only from seed [54,95].
Published information on small sixweeks grass's reproductive biology is scarce,
particularly in regard to seed biology and germination. Further research is
needed on regeneration requirements of small sixweeks grass.

Breeding system/pollination:
Small sixweeks grass is largely
cleistogamous.
Gene flow within and
among populations is minimal to nonexistent due to
cleistogamous habit [54,68]; however, there are occasional
chasmogamous
plants [54].

Seed production:
In a greenhouse study, small sixweeks grass grown in serpentine soil significantly (p=0.05)
increased aboveground vegetative and seed biomass when fertilized with either N-P-K with calcium
amendment or compost with calcium amendment [78]. Information on small sixweeks grass seed production in the
field was not found.

Seed dispersal:
Seed is dispersed primarily by wind [1]. The seed awns provide
a mechanism for possible animal dispersal, although animal dispersal is not
documented.

Seed banking:
Small sixweeks grass maintains a
seed bank [8,101]. On annual grassland at the Hopland Field
Station, California, Vulpia species (V. microstachys, V. bromoides, and V. myuros)
had a mean density of 1,227 seeds/dm²
in 1974 and 438 seeds/dm² in 1975. Mean
seed:germinant ratios were 10:1 and 6:1 in 1974 and 1975, respectively.
Vulpia grasses were pooled due to difficulty of identifying species in the
field [8]. On a serpentine site near Colusa, California,
small sixweeks grass seed density averaged 400/m² [78].

Small sixweeks grass seed tolerates moderate heat for short periods. In a heat tolerance test, 65% of unscarified Pacific
small sixweeks grass seeds that
sustained a maximum temperature of 160 °F
(70°C) for 5 minutes remained germinable
(see Immediate Fire Effect on Plant for
further information on this study) [101].
Plant Response to Fire also provides
further information on fire effects on small sixweeks grass germination.

As an annual, small sixweeks grass cover may fluctuate from year to year [95],
and sometimes no viable seed may germinate in a seemingly favorable germinating season.
On the Hopland Field Station, small sixweeks
grass and other Vulpia species showed "good" germination
at the beginning of the fall growing season, but
viable seed was still plentiful in the seed bank in spring [8].

Soil or litter cover may increase germination. In a greenhouse study, Pacific
small sixweeks grass germination was improved by covering seed
with either 0.3 or 0.5 inch (0.8 or 1.2 cm) of topsoil. Serpentine litter had no effect on
germination. Gulmon [36] suggested that Pacific small sixweeks grass seeds
benefit from the increased wetting time afforded by topsoil coverage. Pacific
small sixweeks grass showed significantly (p=0.007) reduced cover on plots where
mulch was removed compared to plots with intact mulch (9.98% and 25.95%,
respectively) [60].

Seedling establishment/growth:
As of 2006, little information was available on growth rates of small sixweeks
grass. Although some small sixweeks grass ecotypes are adapted to serpentine
soils, the low calcium levels characteristic of such soils may inhibit seedling
root growth [78]. After seedlings at the Hopland Field Station had reached several weeks of age,
they suffered little mortality through winter and spring [8].

Asexual regeneration:
Because it is an annual, small sixweeks grass does not sprout from the root crown after it
produces seed. It dies. However, Vulpia species may die back and sprout from the root crown when wet
weather follows a short-term dry period within the growing season [49].

SITE CHARACTERISTICS:
Small sixweeks grass grows on mesic to dry sites that are often disturbed
[22,42,67]. In Utah it is reported along roadsides and waterways [111].
In Nevada it occurs on open dry or rocky slopes [56]. In Baja California Norte,
small sixweeks grass grows in sands on the dry sides of toeslopes [114].

Soils:
Small sixweeks grass most commonly grows in loose, sandy soils
[67], although it may also grow on clays [42,67].
In California small sixweeks grass prefers open sites,
and is often found on thin or heavily compacted soils [95]. Small sixweeks grass tolerates low-nutrient soils [103].
Desert small sixweeks grass, for example, grows on serpentine or shale
soils [42]. North of San Francisco, Pacific small
sixweeks grass cover was positively
correlated with a low soil calcium:magnesium ratio, which is characteristic of
serpentine soils, although mean plant biomass was lower for Pacific small
sixweeks grass growing on serpentine soils compared to plants on nonserpentine soils [53].
Pacific small sixweeks grass also grows on clay soils with
favorable phosphorus and available water contents [89].

Aspect:
Eastwood small sixweeks grass was most common on southeast-facing slopes (21% frequency)
and least important on northeast-facing slopes (3% frequency)
on annual grasslands of the Jasper Ridge Biological Preserve in San Mateo
County, California. It only
occurred on serpentine soils [70].

Elevation:
Small sixweeks grass is documented at the following elevations:

SUCCESSIONAL STATUS:
Small sixweeks grass prefers open sites [56,57]. It may be found in early to
late succession when the canopy remains open.
For example, it grows on burns in early succession [24,113] (see
Fire Effects and the coastal sage scrub section of
Fire Ecology).
Renner and Allred [86] classify small sixweeks grass as an invader
in late-successional plains grasslands. It tends to increase
with disturbance or when rangeland conditions deteriorate [20]. In old
field succession on a bluebunch wheatgrass-Sandberg bluegrass (Poa secunda) community near
Clarkston, Washington, Pacific sixweeks grass showed trace coverage and 2% to 8%
frequency on young fields (1-12 years since tilling); 1% to 2% coverage and 20%
to 70% frequency on old fields (39-52 years since tilling); and 1% coverage and
35% to 38% frequency on untilled sites [23].

SEASONAL DEVELOPMENT:
Small sixweeks grass is a cool-season species which, depending on geographic
location, establishes in late fall or
early spring, flowers in spring or early summer, then matures, sets seed, and
dies by late spring or early summer.
Germination usually coincides with the beginning of fall precipitation [8].
Phenology of small sixweeks grass across its distributional range is
shown below.

FIRE ECOLOGY OR ADAPTATIONS:Fire adaptations:
Small sixweeks grass establishes from soil-stored seed after fire [25].
No other means of postfire regeneration are documented,
although establishment from off-site wind- or animal-dispersal seed is possible.

Fire regimes:
Fire is important in retaining open structure in
some of the communities where small sixweeks grass is common, but fire was
historically infrequent in other plant communities where it occurs. Frequent fire in palouse prairies
and annual grasslands maintains the grasslands by preventing invasion of woody
plants and reducing litter [82,90,100,115]. Fire plays a more variable
ecological role in shrublands where sixweeks grass is important. Some of the
shrublands (e.g., chamise (Adenostoma fasciculatum) and other chaparral types) depend on moderate-interval
(30-100 years), stand-replacing fire [82]; others are adapted to mixed-severity
fires (e.g., big sagebrush (Artemisia tridentata)) [3,21,71,96]; while some desert shrubland types such as
creosotebush (Larrea tridentata) are poorly adapted to fire [17]. Descriptions of fire
regimes of communities where small sixweeks grass is important follow.

Palouse prairie: Fire frequencies for
bluebunch wheatgrass-dominated habitats vary considerably, depending on the associated
species [7]. Most mean fire intervals are less than 30 years. Estimates for historical fire
intervals in the Snake River Canyon of Idaho for bluebunch wheatgrass-Idaho
fescue-Sandberg bluegrass (Festuca idahoensis-Poa secunda) communities
are 10 to 25 years [51].

Annual grasslands:
Because they are dominated by nonnative annuals, annual
grasslands have no "natural" fire regime. There are no data and few historic
records of presettlement fire return intervals in pristine California prairie.
Probable mean fire intervals (estimates of fire intervals that are derived from
historical or very limited physical evidence) for California prairie are
frequent: approximately every 1 to 2 years. Probable mean fire intervals for
today's annual grasslands are 20 to 30 years [100].

Sagebrush/bunchgrass:
Prior to the 1890s, probably only a few grass species
occurred in early postfire sagebrush (Artemisia spp.) communities of the Great Basin.
Of these, small sixweeks grass and sixweeks grass (Vulpia octoflora)
might have been most important. Generally, native Vulpias would increase
for a few postfire years, then be suppressed by bunchgrasses such as bluebunch
wheatgrass, bottlebrush squirreltail (Elymus
elymoides), and Idaho fescue, and by shrubs such as
basin big sagebrush (A. tridentata ssp. tridentata)
and rabbitbrush (Chrysothamnus spp.) [83]. Historic fire return interval
ranged from around 20 to 100 years [46,115,116]. Cheatgrass and medusahead (Taeniatherum caput-medusae),
nonnative annual grasses, have altered fire regimes and successional
patterns in some sagebrush communities. Fine fuel loads from dry cheatgrass
and/or medusahead can support fire-return intervals as short as 3 to 6 years [83].

Desert shrub:
Small sixweeks grass is a common component
of southwestern steppe communities. For example, it had 40% frequency in a vegetation survey in a
creosotebush-white bursage (Ambrosia dumosa) community in the Mojave Desert [14]. Fire is infrequent in
pristine creosotebush-white bursage, Joshua tree (Yucca brevifolia), and saguaro
(Carnegiea gigantea)communities.
Discontinuity of fine fuels in most years hinders the spread of fire, which was
historically uncommon to rare [15,17,19,48,79]. In most years, pristine stand
structure of these southwestern desert shrub communities is widely spaced woody
plants, bare interspaces, and some perennial bunchgrasses [13,17,18,91].
During wet winters and springs, annuals such as
sixweeks grass increase fuels loads. Biomass accumulations from native annuals
following an exceptionally wet growing season may provide enough
fine fuels to carry a fire in desert ecosystems that otherwise rarely burned [11,102].

Chaparral:
Historic fire return intervals in chamise and mixed-chaparral
ranged from 10 to 90 years [82,101]. Intervals
between fires were longer in communities dominated by nonsprouting shrubs, such
as bigberry manzanita (Arctostaphylos glauca), than in communities
dominated by sprouting shrubs such as chamise [59].

Coastal sage scrub chaparral:
Documentation of historic fire intervals in coastal sage scrub is
lacking. Current fire return intervals vary widely. Total area burned strongly
correlates with precipitation during the previous winter, with heaviest
burning occurring after wet years. Fire is rare following drought [72]. Vogl [108]
estimated an average fire interval of 20 years for
lightning-ignited fire in chaparral adjacent to coastal sage scrub.
Fire severity is generally higher in coastal sage scrub than in seral
chaparral due to higher litter loading and the higher percentage of
terpenes in coastal sage scrub vegetation [34,69].
For a California sagebrush-eastern Mojave
buckwheat (Artemisia californica-Eriogonum fasciculatum) community on the
Cleveland National Forest, California, fire records show that stand-replacing
fire occurs at approximate 28-year intervals. Sixweeks grass is noted in early
postfire succession in the community [113].

The following table provides fire return intervals for plant communities
and ecosystems where small sixweeks grass is important. For further information, see
the FEIS review of the dominant species listed below.

IMMEDIATE FIRE EFFECT ON PLANT:
Fire occurring when plants are mature kills small sixweeks grass [24]. Annual
grasses may sprout from the root crown when fire occurs early in the growing
season [49].

Fire in any season may reduce the seed bank [24]. Small sixweeks grass seed in litter or lying
on the soil surface is most vulnerable to fire kill [101,117].
Most surface fires probably do not harm small sixweeks grass seed that is buried in soil [40,80].
However, even buried seed can die when exposed to heat for long periods of time.
In laboratory experiments, small sixweeks grass seed buried in moist soil died after a 1-hour exposure to 115 to 121
°F (46-49
°C) temperatures [63], while
most Pacific small sixweeks grass seed exposed to temperatures of 160 °F
(70 °C) for only 5 minutes remained viable.
Germination of unscarified Pacific small sixweeks grass seed dropped as follows [101]:

DISCUSSION AND QUALIFICATION OF FIRE EFFECT:
Odion [80] found an insignificant (p>0.05) positive effect of heat on small
sixweeks grass seedling emergence in laboratory tests.
At Vandenburg Air Force Base, California, pre- and postfire soil
samples were collected from a maritime chamise community that had not burned for
at least 75 years (at Site 1) or 50 years (at Site 2). Prefire soil cores were
collected in fall, and both study sites were burned under prescription soon
after. Postfire soil samples were also collected [80]. Fire
intensity was relatively high (see [81] for
fire data). Laboratory treatments for prefire soil samples were a control, heat (100 °C for
7 min.), and heat with chamise charate.
Seedling emergence was counted for pre- and postfire soils samples and in the
field on prescribed burn plots. Mean number of germinants/m² emerging from soil
samples and on burn plots was [80]:

Prefire soil samples

Control

0

Heat

8.8

Heat and charate

Site 1

Site 2

4.4

44.4

Postfire soil samples

0

0

Field emergence on burn

0

0

It is likely that high fire intensities killed small sixweeks grass seed on the prescribed burn sites.

PLANT RESPONSE TO FIRE:
Small sixweeks grass establishes from soil-stored seed in early postfire plant
communities. It is often common after fire [39]. Sampson and others [95]
describe recent chaparral burns as "favorite habitat" for
small sixweeks grass. In California, Sampson and Burcham [94] noted
Pacific small sixweeks grass presence the 1st year after
prescribed burning in chamise and mix-shrub chaparral communities in Mendocino and
Shasta counties. In a survey on
chamise and mixed-shrub chaparral communities of California, Sweeney
[101] found small sixweeks grass was "common on 1-year-old
burns, becoming increasingly abundant on 2-, 3-, and 4-year-old burns." It was
also abundant on open, disturbed sites adjacent to burns [101].

Harrison and others [39] found a significant (p<0.01) soil-fire interaction
for Pacific small sixweeks grass on the California Natural Reserve in northern
California. Pacific small sixweeks grass frequency (%) was highest on burned
serpentine soils [39]:

Soil type

Frequency

burned

unburned

nonserpentine

0.4%

0.5%

serpentine

3.6%

3.1%

Daubenmire [23] found a July 1961 wildfire
promoted Pacific small sixweeks grass near Clarkston, Washington. The fire
occurred in an old field succeeding to a bluebunch wheatgrass-Sandberg bluegrass
community. Percent cover of Pacific small sixweeks grass was low under all
conditions, but relative frequency increased in early postfire years [23]:

Postfire year 2

Postfire year 4

Postfire year 12

Burned sites

Cover (%)

0

1

1

Frequency (%)

0

58

55

Unburned sites

Cover (%)

0

trace

1

Frequency (%)

0

18

25

Often, fire may have only a slight positive effect to no effect on small
sixweeks grass. Small sixweeks grass was present but uncommon on both burned and
unburned sites 6 years after wildfire in a blackbrush community in
southwestern Utah [15]. In a survey of maritime burns, Eastwood small sixweeks
grass had 4% frequency on earl seral burns (postfire years 1-5) in maritime
coast live oak in Santa Barbara County, California. It was not present on
maritime chamise chaparral burns [25].

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:
A July 1961 wildfire had little effect on Pacific small sixweeks grass near
Clarkston, Washington. The fire occurred in an old field succeeding to
rubber rabbitbrush (Chrysothamnus nauseosus)/cheatgrass and bluebunch wheatgrass-Sandberg bluegrass communities.
In the rubber rabbitbrush/cheatgrass community, Pacific small sixweeks grass was not present on burned plots
and had had approximately 1% coverage on adjacent unburned plots.
Mean percent coverage of Pacific small sixweeks grass on burned and adjacent
unburned plots in the bluebunch wheatgrass-Sandberg bluegrass community was [23]:

Postfire year 2

Postfire year 4

Postfire year 12

Burned

Cover (%)

1

trace

1

Frequency (%)

58

2

55

Unburned

Cover (%)

0

trace

1

Frequency (%)

0

18

25

Fall and spring prescribed burning in east-central Oregon had no significant
effect on small sixweeks grass density or frequency in postfire year 1 or 2 [96]. See the
Research Project Summary of this work for more information on fire effects
on small sixweeks grass and 60 additional grass, forb, and woody plant species.

FIRE MANAGEMENT CONSIDERATIONS:
Prescribed and wildfires are most likely to benefit or have no effect on small
sixweeks grass coverage and frequency.
Typically a minor grass favored
by disturbance and varying in cover from year to year, small sixweeks grass is well adapted to establish in most early
postfire environments. Widespread
fire that burns into the soil, killing seed, can reduce small sixweeks grass's ability to recover
from fire. Nonnative annual grasses, which outcompete sixweeks grass
(see Invasives),
can also negatively impact postfire coverage and frequency of small sixweeks grass. A postfire reduction in sixweeks grass
is likely if annual bromes, schismus, and/or lovegrasses are present before fire
or represented in the seed bank.

Small sixweeks grass is sometimes used in seed mixes to reduce postfire erosion [38].
Its effectiveness in doing so has not been tested, although it
is generally recommended for short-term erosion protection (see
Value for Rehabilitation of Disturbed Sites).

IMPORTANCE TO LIVESTOCK AND WILDLIFE:
Overall forage value of small sixweeks grass is generally small due to low productivity [20].
However, small sixweeks grass may show large-volume production in wet years [95].
It usually does not stay green for long [8].

Cover value:Vulpia species provide poor cover for small mammals and birds [26].

VALUE FOR REHABILITATION OF DISTURBED SITES:
Small sixweeks grass is recommended for reclamation and erosion projects [87].
A fast-growing species, small sixweeks grass is used in seed mixes for short-term emergency
erosion control while perennial plants are establishing. In seeding trials in
Riverside County, California, small sixweeks grass did not interfere with growth of other native
species (hollowleaf annual lupine (Lupinus succulentus), California
sagebrush, and eastern Mojave buckwheat)
that were also included in the seed mix [73]. Seeding guidelines for
small sixweeks grass are available [10].

OTHER MANAGEMENT CONSIDERATIONS:Rangeland:
Moderate to heavy grazing may favor small sixweeks grass at the expense of more
palatable perennial grasses [95]. On a clearcut in
northeastern Oregon, small sixweeks grass was slightly more frequent on
cattle-grazed than on big game-grazed plots, showing 4%, 2%, and 3% frequency on
plots used by cattle, big game, and both, respectively [61]. It was also more
common on clipped plots at Carrizo Plain National Monument, California, showing
0.30% on clipped plots and 0.15% cover on ungrazed plots [60]. However,
Pacific small sixweeks grass on the California Natural Reserve
was more frequent on ungrazed than on grazed sites.
On cattle-grazed plots, frequency was 0.3% on nonserpentine soils and 2.1% on serpentine soils,
and 0.6% and 3.3% on ungrazed nonserpentine and serpentine soils,
respectively [39].

Pacific small sixweeks grass greatly increased in cover
following addition of nitrogen fertilizer
on serpentine annual grassland of the Jasper Ridge Biological Preserve,
dominating some fertilized plots to near exclusion of other
species. Density of Pacific small sixweeks grass averaged 290 plants/m²
on fertilized plots and 150 plants/m² on
unfertilized plots. Most annuals (native or not) declined with nitrogen
amendment to the serpentine soil [44].

Invasives:
Nonnative annual grasses can interfere with establishment and growth
of small sixweeks grass. Cheatgrass has relegated small sixweeks grass to
minor status on dry portions of the Columbia Plateau, where
small sixweeks grass was once abundant [66]. In a greenhouse experiment using small sixweeks grass, red
brome (a nonnative species), and pinnate tansymustard (Descurainia pinnata, a native species)
seed from the Mojave Desert, red
brome extracted soil water faster and had higher total plant nitrogen content
compared to small sixweeks grass and pinnate tansymustard. Red brome also showed higher
germination rates compared to small sixweeks grass and pinnate tansymustard,
although small sixweeks grass produced more total seed. A growth chamber study showed
biomass of small sixweeks grass was significantly (p<0.01) reduced when grown
with red brome in nitrogen-fertilized desert soil compared to small sixweeks
grass grown with red brome in unfertilized desert soil [93].

A field inventory and follow-up experiment in grasslands north of San Francisco
showed evidence of growth interference from nonnative annuals, and also showed
that Pacific small sixweeks grass shows ecotypic differences. Pacific small
sixweeks grass was most common (and dominant) on rocky serpentine slopes, intermediate on serpentine
meadows (which were dominated by native forbs), and least common on
nonserpentine grasslands (which were dominated by nonnative annual grasses). On
plots treated with herbicide and seeded with Pacific small sixweeks grass
collected from nonserpentine sites, total Pacific
small sixweeks grass
seedling emergence and survival was greatest on nonserpentine soils and lowest
on serpentine soils. However, Pacific small sixweeks grass seed from rocky
serpentine slopes showed best emergence and survival on
serpentine soils [53].

101. Sweeney, James R. 1956. Responses of vegetation to fire: A study of the herbaceous vegetation following chaparral fires. University of California Publications in Botany. [Berkeley, CA: University of California Press]. 28(4): 143-250. [3776]